Examples of families (g_λ)_λ of calibration functions. In Fig. 4a (additive calibration), λ ranges from −∞ to +∞ with λ₀ = 0, whereas in Figs. 4b (multiplicative calibration) and 4c (chi-squared calibration), λ ranges from zero to +∞ with λ₀ = 1. In Fig. 4c, the number k of degrees of freedom is set to three, the scaling factor a is set to 0.01, and the multiplicative factor b is set to the maximum value such that g_λ remains non-decreasing for any λ ≥ 0, that is, b ≈ 0.041. (a) g_λ : r ↦ max(r + λ, 0), (b) g_λ : r ↦ λr, (c) g_λ : r ↦ r + bF_X²(k)(r/a)(λ − 1).